I. Field of the Invention
The present invention relates to Ground Runup Enclosures (GRE) which are used at airports to run jet engines up to full power or thrust in order to test the condition of the engines. The purpose of a GRE is to protect the airport and surrounding area from the force of the blast from the jet engines and from the great amount of noise created by the engines at full runup. The instant invention pertains to aerodynamic enhancements to a GRE which allow stable flow of air to the jet engine inlets under varying wind velocities and directions.
II. Description of Related Art
For more than 30 years, airports, airlines, and maintenance companies have been faced with the problem of trying to mitigate the noise generated during engine ground runups. In the 1960's the most popular technology involved large "mufflers". This approach involved permanently fixed mufflers or detuners. To utilize this type of facility, a tow motor would be attached to an aircraft, and it would be pushed back adjacent to the detuners, so that the jet nozzle would be immediately adjacent to, or slightly inside of the detuner. There were several significant disadvantages to this arrangement: First, the detuners were aircraft specific thus requiring an airline such as British Airways to have many sets, each for a different type of aircraft. Second, there are great operational risks, difficulties and liabilities associated with positioning a multi-million dollar aircraft next to a fixed piece of ramp equipment. It is also very time consuming. Finally, the aircraft can only utilize these fixed detuners for full takeoff power runs if the wind is within certain limits, generally about 30 degrees of the nose. U.S. Pat. No. 3,386,528 describes such an invention in which the jet engines are plugged into curved tubular deflectors which direct the jet blast and sound upward into the atmosphere.
In the early 1980's, a German firm developed a new type of noise protection facility. The German firm manufactures industrial noise panels generally for use in industry. In about 1982, they applied this technology to aircraft by building an engine ground runup facility comprising a four (4) sided enclosure whose end and walls support a matrix of rectangular boxes. The boxes which are made of metal or concrete have openings in the front to admit sound waves. The boxes contain sound absorptive material to deaden the sound. The walls of these units have generally been of quite heavy construction, the walls being constructed of structural materials such as concrete. The front of the facility was comprised of doors which moved on rails. Initially, these facilities were used primarily for low bypass engines as used on older aircraft. These engines are far more tolerant of irregular winds than are the high bypass engines used first on the B-747. The German firm has built about 6 or 7 of these facilities. As these facilities came to be used with high bypass engines, users generally found that their usability was greatly diminished, because whenever the wind was strong and not coming directly into the enclosure, the high walls would create turbulence which could induce surging and create a compressor stall in the high bypass engine. This has become a common problem for all GRE's with solid side walls.
That same German firm has tried several facilities with vertical louvers in the side and front walls, but these louvers, too, have proven to be unsuccessful in solving the problems of turbulence within the facility.
Another primary problem with the GRE designed by the German firm is with recirculation of the air through the engine inlet. They use a screen type diffuser instead of a true blast deflector within their facility. This expanded metal screen slows down the blast, while assisting acoustically, but the mass of air moving more slowly after being diffused, is prone to be blown back towards the engine inlet during side and quartering rear wind conditions. If the same exhaust air is recirculated, it can cause surging or stalling, as the oxygen of the mass has previously been burned by the engine.